Ink jet printers have become a very common way for printing images from a computer. Ink jet printers work by spraying small drops of colorants (ink) onto a receiver to form an image. Typically, ink jet printers use four or more different colors of colorants to produce colored images. Most commonly cyan (C), magenta (M), yellow (Y), and black (K) colorants are used. Sometimes additional colorants such as red, green, blue, orange, light cyan, or light magenta are also used. A given set of colorants, together with the writing system used to spray the ink on the receiver, will have an associated color gamut, which is defined to be the set of colors that can be made using the printer. The different colors within the color gamut can be made by adjusting the amounts of the various colorants that are applied in a given region of the print.
One problem that has been common in ink jet printers is an artifact commonly referred to as “ink bleed.” Ink bleed occurs when ink that is sprayed on the receiver in one location spreads laterally on the page to a region where it is not wanted. Ink bleed can result if too much ink is applied to the page in a given location such that the receiver cannot absorb the ink and it forms a puddle on the surface, which can then seep laterally.
Another source of bleed is due to differences in the chemical formulations of the inks. Typically, the chemical formulations of black inks are quite different than the chemical formulations of the colored inks. These differences can make the image particularly susceptible to bleed at interfaces between regions where black ink is applied, and regions where colored ink is applied. An example of this would be printing black text on a yellow background, or printing a pie chart having colored segments with a black border. An illustration of such an interface is shown in FIG. 1A. Here a first region 10 comprised of a large amount of black ink is adjacent to a second region 11 comprised of a large amount of colored ink, such as cyan, magenta, or yellow. The term “large amount” refers to an amount of ink sufficient to result in bleed artifacts. FIG. 1B illustrates the appearance of ink bleed artifacts 13 that can occur at the interface between the first region 10 and the second region 11. In this example, the black ink from the first region 10 can be seen to have seeped into the colored ink in the second region 11. However, bleed can also happen in the reverse direction as well. Often the bleed artifacts 13 take the form of small “fingers” of ink that grow out from one region to the other.
It is also common for the colored inks to have quite different chemical formulations from each other, resulting in variation of the bleed artifacts from color to color. For example, the bleed artifacts between black and cyan may be of lesser magnitude than the bleed artifacts between black and yellow, due to differences between the chemical formulations of the cyan and yellow ink.
There have been a number of approaches disclosed in the prior art to address this problem. In U.S. Pat. No. 5,168,552, Vaughn et al. disclose a method where composite black is changed to true black ink except when black dots are within a minimum spacing from color dots.
In U.S. Pat. No. 5,428,377, Stoffel et al. disclose a method for adjusting what ink(s) are used to print black image areas depending on whether the surrounding pixels contain black, colored, or blank content.
In U.S. Pat. No. 5,568,169, Dudek et al. disclose a method for adjusting usage of slow- and fast-drying black inks depending on whether the surrounding pixels contain any colored inks. The slow-drying ink is either totally replaced, or is selectively replaced.
In U.S. Pat. No. 5,570,118, Rezanka et al. disclose a method for reducing ink bleed by producing a small gap between a slow-drying black ink region and a fast-drying color inks region. In one embodiment, the gap is filled in with a fast-drying second black ink.
In U.S. Pat. No. 5,596,355, Koyama et al. disclose a dot judgment circuit for determining whether to print black pixels using a slow-drying black ink or fast-drying colored inks depending on whether color image content is surrounding the black pixels.
In. U.S. Pat. No. 5,635,967, Klassen discloses a method for reducing ink bleed for a binary image that involves blurring the binary image to form a continuous tone image, detecting edges in the continuous tone image, and reducing the number of pixels printed on the edge in the original binary image.
In U.S. Pat. No. 5,699,492, Karaki discloses a method for changing from pure black pixels to composite black pixels for black areas that are in contact with color areas.
In U.S. Pat. No. 5,751,310, Yano et al. disclose a method for replacing black ink with a process black in a border region where black and colored regions are adjacent. The border region is detected using an expansion operation.
In U.S. Pat. No. 5,809,215, Heydinger et al. disclose a method for reducing ink bleed whereby black pixels are altered when a certain fraction of nearby pixels contain colored ink. Methods for altering the black pixels include removing selected pixels or removing all of the pixels.
In U.S. Pat. No. 5,975,678, Kanematsu et al. disclose a method for selectively replacing black ink with colored inks depending on the proximity to colored regions. The degree of proximity is determined by doing a weighted sum according to an array of distance-weighted coefficients. Depending on the degree of proximity, more or less ink is substituted.
In U.S. Pat. No. 5,992,971, Takahashi et al. disclose a method whereby ratio of black and colored is adjusted according to the color content of nearby marginal pixels. In some embodiments, the amount of adjustment is dependent on distance between the current pixel and the marginal pixel.
In U.S. Pat. No. 6,007,182, Matsubara et al. disclose a method for adjusting what ink(s) are used to print black image areas depending on whether any surrounding pixels contain colored image data. In areas adjacent to colored regions, black is made using CMY inks. Otherwise, black ink is used.
In U.S. Pat. No. 6,015,206, Heydinger et al. disclose a method where ink bleed is reduced by printing process black and black ink in an alternating pattern for dots on the boundary between black regions and color regions.
In U.S. Pat. Nos. 6,084,604 and 6,312,102, Moryiama et al. disclose a method for adjusting what ink(s) are used to print black image areas depending on whether any surrounding pixels contain colored image data. In areas adjacent to colored regions, black is made using CMY inks, and using black ink elsewhere.
In U.S. Pat. No. 6,118,548, Ryan discloses a method for replacing black ink with a process black for regions near colored pixels. A logical search sequence is used to identify the nearest colored pixel.
In U.S. Pat. No. 6,164,756, Takahashi et al. disclose a method for reducing bleed by using a multipass mode for image regions where a boundary between a black image region and a colored image region is detected, and a faster single pass mode otherwise.
In U.S. Pat. No. 6,259,536, Coleman discloses a method for determining whether to use black ink or process black to print a black object depending on whether the black object is on a colored background.
In U.S. Pat. No. 6,270,186, Smith et al. disclose a method for reducing ink bleed in a multilevel ink jet printer capable of printing multiple numbers of drops at a given pixel location by reducing the number of pixels printed with more than one drop in a black/colored border region.
In U.S. Pat. No. 6,361,144, Torpey et al. disclose a method for reducing intercolor bleed using a color pixel modification pattern to remove a fraction of the color pixels near a color/black boundary, and using a black pixel modification pattern to replace black ink pixels near a boundary with colored inks.
In U.S. Pat. No. 6,412,938, Markham et al. disclose a method whereby bleed is reduced by printing black ink in a multipass mode using a larger print head, and colored inks are printed in a single-pass mode.
In U.S. Pat. No. 7,234,791, Couwenhoven et al. disclose a method of reducing intercolor bleed using a spatial filter applied to the black channel to identify a color/black boundary, and then removing a portion of the colored ink near the boundary.
In U.S. Pat. No. 7,173,734, Klassen, et al. disclose a way for intercolor bleed reduction in liquid ink printers which uses an edge detection operation to find edges in the image and determines a reduction factor for edge pixels based on the ink coverage level.
Many modern inkjet printers now have the ability to perform basic image processing operations inside the printer, either using a small CPU or a dedicated hardware ASIC to perform the image processing. As such, the image processing is not required to be performed on the host PC attached to the printer, and the host PC driver can simply send the source image data directly to the printer (usually in an RGB data format) for processing and printing. However, the printer ASIC typically does not contain an algorithm for applying intercolor bleed control, and the CPUs typically used in inkjet printers often do no have sufficient processing power to implement such an algorithm in software. Therefore, there is a need for an algorithm to control intercolor bleed that can be run in a host PC driver, and can operate on a source image in RGB color space.